My name is Cassie. I can't tell you my last name. I wish I could. It's kind of a nice last name. And I can't tell you where I live or the true names of my friends. Why? Because the enemy never stops looking for us. The enemy. The Yeerks. They're everywhere. The Yeerks: a parasitic species from a far-distant planet. All they are is little gray slugs, really. I've seen them in their natural state. They look like big snails without the shell. You could squash one under your foot and it would be helpless to stop you. But the Yeerks don't live out their lives as slugs. Like I said, they are parasites. See, they enter the head of another species, flatten themselves out, and wrap themselves around the brain. And then they take control.